As for a memory using a phase-change material, for example, the following technologies have been studied by the inventors of the present invention.
A phase-change memory which is a memory using a resistor element formed of a phase-change material is also a non-volatile memory in which the phase-change material is crystallized through a set operation and amorphousized through a reset operation, thereby storing information based on a difference in resistance values due to the change of phase state of the phase-change material. Here, the set which is a low resistance state does not necessarily be a completely crystallized state, and the reset which is a high resistance state does not necessarily be a completely amorphosized state, and the state can take an arbitral value between a value in the low resistance state representing the completely crystallized state and a value in the high resistance state representing the completely amorphosized state.
For the reset, a high voltage is applied to increase the temperature of the phase-change material to a temperature equal to or higher than its melting point. In addition, after melting the phase-change material, a short-time pulse which rapidly attenuates is applied in order to prevent crystallization. For the set, the phase-change material is held at a temperature equal to or higher than its crystallization temperature and lower than the melting point. For this reason, a set pulse is lower in voltage and longer in time than the reset pulse.
What the phase-change memory can be applied to is replacement of the FLASH memory which is the mainstream of non-volatile memories. Since the phase-change memory can be operated by a lower voltage and is capable of high-speed rewrite as compared with the FLASH memory, the phase-change memory can be a higher-performance non-volatile memory. And if speed enhancement goes further, a high-speed non-volatile RAM can be achieved. While many of portable devices have both a non-volatile FLASH memory and a DRAM which is a high-speed volatile RAM mounted thereto, if a non-volatile RAM having features of these two memories can be achieved, the FLASH memory and the DRAM can be integrated as one chip, thereby replacing all the semiconductor memories.
Note that, examples of technical documents relating to the present invention include Patent Document 1 and Non-Patent Document 1.
Patent Document 1: Japanese Patent Application Laid-Open Publication No. 2003-100085
Non-Patent Document 1: Japanese Journal of Applied Physics, Vol. 30, January, 1991, pp. 97-100